(1) Field of the Invention
The invention relates to the fabrication of integrated circuit devices, and more particularly, to a method to further improve the imaging of patterns that are used in photolithography by providing improved enhancement effects for sub-resolution lines that are added to a line pattern, to address issues of having insufficient space in order to add sub-resolution lines and issues of avoiding printing sub-resolution lines.
(2) Description of the Prior Art
The creation of semiconductor devices requires numerous interacting and mutually supporting disciplines. Addressed at this time are the disciplines that are required to create patterns on a semiconductor surface, such as the surface of a layer of photoresist or the surface of a semiconductor substrate.
Since device features are transposed from a mask onto a semiconductor surface using photolithographic imaging processes, which requires the transfer of photo energy from a source to a target surface, it is to be expected that, for target features that are created in very close proximity to each other, the transfer of photo energy interacts for very closely spaced device features, most commonly interconnect lines having sub-micron spacing between adjacent lines. This interaction imposes limitations on the proximity of adjacent device features, these limitations are referred to as Critical Dimensions (CD) of a design and device layout. This CD is commonly defined as the smallest spacing or the smallest line width of an interconnect line that can be achieved between adjacent interconnect lines. This CD in current technology is approaching the 0.1 to 0.2 μm range.
The invention addresses the problems of insufficient resolution and depth of focus in imaging interconnect lines and the spacing that is provided between these lines. In past practices, these problems have been addressed by adding sub-resolution lines in combination with off-axis illumination. The latter improves depth of focus for closely packed lines. The sub-resolution scattering bars artificially produce close packing while the scattering bars are not being printed. The latter is due to the fact that the size of the scattering bars are below the resolution limit. This method is therefore limited by the small size of the scattering bars. Increasing the size of the scattering bars in order to enhance the resolution and depth of focus results in printing these assist features. An improved method is therefore required which addresses these issues and the issue of printing of assist features.
U.S. Pat. No. 5,1424,770 (Chen et al.) reveals a mask for reducing Proximity effects using leveling bars.
U.S. Pat. No. 5,821,014 (Chen et al.) shows an OPC method using scattering bars.
U.S. Pat. No. 6,218,089 (Pierrat), U.S. Pat. No. 6,197,452 (Matumoto), and U.S. Pat. No. 6,109,775 (Tripathi et al.) are related photo processes using extra shapes to improve resolution.